Relay system monitoring



JUIY 29, l941- A. N. GoLDsMlTH n 2,250,950

RELAY SYSTEM MONITORING Filed Dec. 9, 1939 3 Sheets-Sheet l STA. w.574.4 /6

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ATTORNEY IRM/souci@ /ffrsk July 29, 1941.

A N. GoLDsMn-H 2,250,950 RELAY SYSTEM MONITORING Filed Dec. 9. 1939 :ssheets-sheet 2 Ely. 6 ST4. E

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ATTORNEY Patented July 29, 1941 UNITED STATES PATENT oEFlcE RELAY SYSTEMMONITORING Alfred N. Goldsmith, New York, N. Y.

Application December 9, 1939, Serial No. 308,388

s claims. (c1. 25o- 15) This invention relates to remote control systemsfor radio relay stations, and has more particularly to do with a deviceof this character which is suitable for controlling a radio relaystation from a distant terminal station, and also to control a chain ofsuch relay stations by remote control signals from either one of twoterminal stations at the endsof the chain.

While my invention has utility in a great variety of different remotecontrol systems, it may be best illustrated by its use in connectionwith typical ultra-short wave radio relay systems for the transmissionof communications, such as messages, sound broadcast programs, ortelevision broadcast programs.

According to present practice it is necessary in transmittingcommunications over ultra-high frequency channels to locate a number ofrelay stations along a route, so that the maximum distance oftransmission of the radiant energy from one station to another shall bepreferably no greater than the line of sight. Obviously, if the,transmitters and receivers can be located at elevated points withinsight of each other, highly directional antennas may be used to securethe requisite and desirable power gain in the chosen relay direction.The relay stations themselves may in general be located at distancesbetween 10 and 50 miles apart, depending upon terrain receivingequipment (and preferably only one receiver) shall be active at alltimes in each relay station.

A relay system such as the above is vulnerable to an occasionalbreakdown or sub-normal operation in one or more of its individual relaystations. Ii, however, a single relay station breaks down along thenetwork or system, serious and objectionable conditions arise. In therst place, the signal is lost at the distant end of the system. in thesecondY place, there is no speedy means, in the system itself, fordetermining where the break or decient operation has occurred. Thus itbecomes difficult to know where to send a repair crew. In the thirdplace, if the.

operation of a relay station becomes decient in introduction of noise)Vthere is no means of determining readily by means ofthe System itselfwhere imperfect operation is originating. Thus there may be long andcostly delays and explorations on such a relay system under such condi#tions.

Another limitation of existing networks is the fact that the unmannednetwork must, in general, be used as a unit from end to end, and that itcannot be shortened if desired by terminating it at some speciicstation. Still another limitation of present relay systems is that thereis no way of monitoring the operation of all or a part of the relaysystem from one or both terminal stations thereof. Further, presentlyused relay systems in general are one way and cannot readily be made oneway or two way at will from one or both terminals.

It is the object of the present invention to overcome the limitationsmentioned above. The objects of the invention thus include thefollowlng:

(a) Means whereby a break or discontinuity of service in the network atany point thereon canspeedily be located (and in some cases partl orentirely diagnosed as to its cause).

(b) Means whereby the particular relay'station in which a deficiency ofquality in relaying occurs may be readily determined from the ter; minalstation.

(c) Means whereby the network can be started up, relay station by relaystation, from a terminal thereof, the operation of the system for eachportion of increasing length thereof being also determinable at the saidterminal station.

(d) Means whereby an extensible test loop,

extending as far along the system as desired, canV tween times of activeoperation may be secured.

('g) Means whereby certain failures or derl-v ciencies in individualrelay stations may be identied and studied at a terminal station.

The invention itself and the preferred methods to be employed incarrying it out may best be understood by the following description whenread in View of the accompanying drawings, in which Figure 1 showsdiagrammatically the interrelationship between a plurality ofultra-short wave stations each having its appropriate transmitterortransmitters for radiating energy of an appropriate ultra-highfrequency;

Fig. 2 illustrates also diagrammatically an operating condition in whicha station in the west controls a relay station in a direction easterlytherefrom for the transmission of its traflic signals further east;

Fig. 3 illustrates an operating condition in which a station in the westsets up at an easterly station the proper conditions for recording thecommunication thereat while causing the easterly station to re-radiatean identifying monitoring signal on its own carrier wave back to theoriginal sending station;

Fig. 4 illustrates how a terminal station in the west may transmit asuccession of suitable signals such as will set up through connectionsfor relaying a communication over successive easterly bound links of aradio network;

Fig. 5 illustrates the operating conditions at three stations in achain, such as will enable the westerly terminal to transmit acommunication through an adjacent easterly relay station, and thence toa station further east, where it is recorded and caused to transmit backa monitoring signal, which is ultimately received at the westerly pointof origin of the communication;

Fig. 6 illustrates the operating 'conditions to be obtained in a two-wayradio network which comprises at least two relay stations intermediatebetween the terminal stations;

Fig. '7 illustrates another operating condition in which communicationsmay be originated simultaneously at each of two terminals andtransmitted over different links of the network;

Fig. 8 shows diagrammatically how a low-power receiver operating undercontinuous service conditions, may be employed in response tostartand-stop signals for controlling the feeding of energy to aplurality of ultra-high frequency receivers, the object being toconserve power during stand-by periods; and

Fig. 9 illustrates in considerable detail a preferred circuitarrangement of relaying and switching apparatus to be used at a singleremotely controlled relay station.

Referring first to Fig. 1, I have indicated by block diagrams differenttransmitters and receivers at each of four stations. The west terminalstation W comprises a transmitter WT capable of feeding a carrier wave uto a transmitting antenna l. The west terminal station also comprises areceiver WR1 which derives its signals from a receiving antenna 2. Inthis case it is indicated that the carrier wave to be received is onewhich may be designated ua, because it originates at station A and issent out by a transmitter AT1 located at station A.

In like manner different receivers and transmitters are shown in theblocks appropriately grouped as being comprised in either station A,station B, or the east terminal station E. Thus the transmitter AT atstation A is adapted to radiate signals superposed on a carrier wave u',while the transmitter BT at station B radiates the carrier u". Likewise,for transmitting communications from east to west transmitter ET1radiates a carrier wave ue which is received at station B by the antennaconnected to receiver BR1. Re-transrnission from station B on carrier ubis obtained. by the operation of transmitter BT1, this wave beingreceived at station A by receiver AR1.

,In Fig. 1 the four units at Station A. are

shown inter-connected by dotted lines to indicate that under differentconditions they may be inter-connected in different ways. Thus, when itis desired that a communication shall be sent through station A from apoint of origin at the west terminal and proceeding in a directionfurther east, then the receiver AR will be arranged to control thetransmitter AT. However, if it is desired for test purposes, a signalfrom the west terminal may be reverted by station A back to the point oforigin, receiver AR being then caused to control transmitter AT1.

A further possibility exists in testing the operativeness of a series ofunattended relay stations as shown in Fig. 1. Assume, for example, thatit were desired to transmit a message from the west terminal transmitterWT through stations A and B to the east terminal receiver ER, but thatfor some reason or another the messages do not go through. It is thennecessary to locate the particular relay station or terminal which hasfailed. To do this a monitoring signal may be sent out from the westterminal transmitter WT under conditions which, if there were no breakin the chain, would be successively relayed to the east terminal whereit would be reverted after being keyed with the signature of the eastterminal and would proceed over the links of the channel which includethe transmission carriers ue, ub and ua, the latter arriving at the westterminal receiver WR1. If this monitoring signa fails to come through,then a remote control signal may be transmitted which operates switchesat station B for controlling the transmitter BTi directly from thereceiver BR. The reverted monitoring signal is then to be keyed by asignature code appropriate to station B. If this signal fails to comethrough to the west terminal, still another switching operation may beperformed at station A whereat the transmitter AT1 is placed underdirect control of receiver AR. Here an unkeyed monitoring signal istransmitted easterly over only one link, is then keyed and retransmittedwesterly over only one link. Thus, wherever it is found that a signalcan be reverted it is known that a failure of operating equipment hasoccurred beyond that point. At times it may be desirable to check theoperative conditions at relay stations from both directions, that is, bysending out an unkeyed monitoring signal from each terminal (but ingeneral not at the same time, since they would interfere with oneanother), thereby to test the inter-connections between receivers andtransmitters at each of the relay stations. This, of course, can bereadily accomplished as will be indicated more in detail in thedescription to follow.

Referring to Fig. 2, I illustrate a portion of a radio network whichcomprises a west terminal having a transmitter WT whose antenna l isaimed toward a receiving antenna 3 located at relay station A. Thediagram is intended to illustrate the use of a remote control signal forestablishing connections between the receiver AR and the transmitter ATat station A, whereby the communication may be relayed in an easterlydirection from antenna 5. As will be shown hereinafter, the carrier waveu which is appropriate to the west terminal transmitter, may havesuperposed thereon a tone frequency or a code signal of any desiredcharacter, indicated in the diagram as st, for operating a suitablerelay at station A, thereby to establish the necessary connections.After this signal st has been transmitted it is then possible tocontinue operation of the transmitter WT for sending out a message, abroadcast program, or the like, in an easterly direction, so as to bere-radiated by the transmitting antenna at station A.

Referring to Fig. 3, I show how a test of operating conditions atstation A maybe made by remote control from the west terminal. In thiscase it is preferable to send out a relay setting signal sl forestablishing the control of the transmitter AT1 from receiver AR, bothat station A. Receiver AR has connected thereto a recorder and also akeyer, the latter being interposed between the receiver AR and thetransmitter AT1. After the switching signal sl has lbeen sent, amonitoring signal m may then be superposed on the carrier from thetransmitter WT, and this monitoring signal, after reception at AR, iskeyed with the signature which identifies station A, and then caused tocontrol transmitter AT1 for reverting the monitoring signal to the westreceiver WR1. It should be understood that since station A transmits ona different carrier wave than the west terminal, the monitoring signal mwill preferably be demodulated and then keyed as monitoring signal mafor modulating the carrier wave ua.

Fig. 4 illustrates a system in which it is required that each of twostations A and B shall be successively remotely controlled by signals stand st originating at station W, the west terminal. The signal stestablishes connections between the receiver AR and the transmitter ATat station A. The signal s't then Afollows through station A and is sentout therefrom to control the establishment of connections betweenreceiver BR and transmitter BT of station B. After these connectionshave been made, it is possible to transmit the communication fromstation W through station A and out of station B on antenna 8.

Fig. 5 illustrates a system in which it is possible to transmit asuccession of switching signals and a monitoring signal for testing theoperating conditions at each of two unattended relay stations A and B.The transmission of switching signal st from the transmitter WT atstation W establishes connection between receiver AR and transmitter ATat stationv A; Then follows the transmission of `a further switchingsignal sl which follows through station A and is received at station Bfor establishing inter-connection thereat from the receiver BR through akeyer to the transmitter BT1. After these connections have been made, anunkeyed monitoring signal m transmitted from station W is relayed bystation A to station B, where it is keyed with the signature of stationB and caused to control theV transmitterv B'I1 for reverting a keyedmonitoring signal through station A and thence to receiver WR1 atstation W. Obviously, the same principles apply for an extension of thistest signal system as far as there may be connecting links between aterminal station and a remote relay station. When keying is referred toherein, it should be understood to cover broadly the impressing of anydesired identiable characteristic on the carrier wave by a modulationprocess.

Fig. 6 illustrates how the various receiving and transmitting unitswhich are preferably provided F at each terminal and at each of a seriesof relay stations may be employed simultaneously for two-waycommunications. In this case a communication designated cw originates atstation W, and is transmitted successively over the difsoi ferventinter-connecting linksV between that station and station A, thence tostation B, and nally tov station` E whose receiver ER controls arecorder or other utilization device. Simultaneously a communicationdesignated ce may originate at station E where it is sent out from thetransmitter ET, and is passed through stations B and A successively,thence to be transmitted to and recorded at station W. It is to beunderstood in'this connection that the east-bound and westbound channelsmay be entirely separated from one another, as shown in the diagram,merely by setting up the proper inter-connections and controls at eachrelay station. 'I'he carrier waves to be employed for east-bound trafcare, in general, distinct from the carrier waves to be employed forwest-bound traflic, so that no interference between the east-bound andwest-bound communications occurs.

Fig. 'I will now be referred to for showing how different links of aradio network may be simultaneously employed when it is not requiredthat a communication shall be sent clear through fromv one terminal tothe other. Reference to the drawings will indicate that it maybe desiredto send a communication originating at station W only so far as stationA, where it may be recorded. It will be understood that the recorder orrecorders here used are of a type suitable for the corresponding type ofcommunication, e. gf, an ink-Siphon recorder for telegraph signals, forprinter telegraph signals, a phonograp-hc disc recorder for telephonesignals, a motion-picture camera recorder for television signals,orequivalent devices. In order-t0 monitor the communication designatedcw it is preferable to interconnect the receiver AR and the transmitterAT1 so that the signal itself may be reverted back to receiver WR1 atstation W.

While the communication .cw is being'transmitted, it is possible toemploy other links of the radio network, say, for example, by sendingout a communication ce from the transmitter ETl at station El, thistransmission being relayed through station'B to the receiver AR1 atstation A, provided this station is equipped with a second recorder; Thecommunication ce may alsobe reverted and sent back to station E overeast-bound linksrof the network. Hence the various links may be checkedfor operativeness duringtimes when stations A and B are unattended.

Fig. 8 isnow referred to for showing a simple system in which it ispossible to conserve power at any one of a plurality 0f radio stationswhich for the most part remain unattended. It is to be understood thatany receiving equipment, which is to be utilized under heavy traiicconditions, will require the expenditure of considerable power forlament heating of the .discharge tubes and for plate current therein. Itis desirable, therefore, that these receivers be turned off when notraflic requirements are imposed thereon. It is possible, however, toequip each radio relay station with a stand-by receiver which shall atall times be receptive of appropriate incoming signals. The receiveritself may be fed with energy from an omni-directional antenna l, ifdesired. Furthermore, it may be preferable to employ signalling waves inthe lower range of high frequencies in order to reach greater distancesfrom the terminal to any number of relay stations in a given network.For the sake of simplicity it may be assumed further that one receiver8, located at each relay station, may be suicient for applying iilamentvand plate potentials'to each and all of the ultra-high frequencyreceiving units located at a given relay station. Under these conditionsit is sufficient for the receiver B to respond to a predetermined signalhaving a selective modulating frequency superimposed thereon such aswill be passed by a filter 9 for controlling a relay I0, to throw itsarmature II against the contact I2 so that power from the source I3shall be applied to each of the receivers R and R1. The relay I9 ispreferably polarized so that its armature I`I will, after movement toone side or the other, remain in the position in which it is set untilmoved in the opposite direction by reversal of the magnetism in therelay core.

Assuming that the receivers R and R1 have been placed in operation by astart signal having a given frequency characteristic for being passedthrough the filter 9, and that the lower winding of the relay IU hasbeen energized to pull the armature I I against the contact I2, thiscondition may continue indefinitely as long as it is desired to operatethe receivers. The transmission of a stop signal having a modulationfrequency characteristic diiferent from that of the start signal will bepassed through filter 9a and cause the upper winding of the relay I tobe energized, thus restoring the armature II to the position shown inthe drawings, whereat the power circuit through the contact I2 is openedand the receivers R and R1 are shut off. It is to be understood thatvarious equivalent means for selecting the stop and start signals whichpass through units 9a and 9 may be adopted. Thus units 9a and 9 may becode selectors responsive in each instance only to a particular keyingsuccession of dots, dashes, or both. Otherwise stated, any practicalforms of distinctive modulation of the carrier for actuating 9a and 9may be substituted for the tone modulations hereinabove described.

It will be obvious to those skilled in the art that various changes maybe made in the particular circuit arrangement shown in Fig` 8 for thepurpose of switching the power on and off at an unattended relaystation. Among the alternative arrangements are those which would notnecessarily require the use of an omnidirectional antenna. In certaininstances a stand-by receiver having ultra-high frequency apparatus fordetecting a highly directional beam signal may be used, if desired. Inany event, however, it is preferable to conserve power at a stationwhich is unattended by providing a lower'power receiver or one whichdoes not consume an appreciable amount of power in the absence ofsignals,.this receiver being available at all times for starting upother receiving and possibly transmitting equipment for the interchangeof traffic Signals. As an example of apparatus of this type, referenceis made to United States Patent #1,731,983, granted October 15, 1929 toCharles E. Prince, and entitled Electric call apparatus. In the patentmeans are shown which are responsive to signalling energy and which donot require a wasteful consumption of tube filament power duringstand-by periods. The apparatus therein disclosed operates in suchmanner that when a signal is received, it is rectified withoutamplification, thereby operating a sensitive relay which closes filamentand plate circuits for auxiliary apparatus in the receiver so thatdependable reception may thereafter be obtained. Improvements over thesystem of Prince are also known in the art. Receivers such as thatdisclosed in I-Ioll-l of theInstitute of Radio Engineers, 1938, pages.,

818 to 825. f

Referring now to Fig. 9, I show therein a circuit diagram which willexplain more in detail my preferred mode of operation of an unattendedradio relay station. In this diagram, for the sake of simplicity, thecircuit arrangements of Fig. 8

are omitted, since it may be assumed that apparatus equivalent to thatof Fig. 8 will be employed wherever it is required to start and stop theoperation of the receivers R and R1 (Fig. 9). Receiver R has connectedthereto an antenna I4 which is aimed to receive signals from a stationto the west. Receiver R1 likewise is connected to an antenna I5v forreceiving signals from a station to the east. In the upper right-handcorner of the diagram a transmitter T is shown having an antenna I6facing to the east, and in the lower lefthand corner is a transmitter T1having an antenna I'I facing to the west.

The circuit arrangements are substantially duplicated in order thatcontrol of the relay station may be had from a remote station either tothe west or to the east. It will be sufficient, therefore, for purposesof understanding the diagram, to describe the operation of the system ascomtrolled by signals from the station to the west of the relay station.

Connected with the output side of the receiver R, I preferably employthree devices t, l, and 1' which may, if desired, be in the form of tonefrequency filters, or alternatively they may be in the form of codeselectors. It is to be understood, therefore, that these devices may bevaried to suit the circumstances under which the relay station is to beoperated. For the sake of simplicity however, devices t, l and 1' willbe hereinafter mentioned as selectors or lters.

Associated with these selectors are two polarized relays I8 and I9, eachrelay possessing two windings, one for actuating the armature in onedirection, and the other for actuating said armature in a reversedirection. The normal position of the armatures is shown in the drawingsas an open circuit position for the circuit to be controlled. Selector tresponds only to a given type of signal and actuates relay I8 forclosing a circuit from battery 20 to relay X. This relay is used toestablish suitable connections for passing signals through the relaystation and out on a communications link further east thereof. Thetraffic signals which will follow the operation of the selector relay Xwill, of course, be of a type which will be blocked by the selector t aswell as by the other selectors l and r. Hence the relay I8 will remainin its operating position during the transmission of traiiic signals ofany desired character. Also the relay X will remain energized duringsuch a period.

The through-circuit connections preferably include the following:Armature a of relay X is connected to a power supply 2| for energizingboth of the transmitters T and T. The object attained by energizing bothtransmitters is to enable the operation of the relay station to bemonitored from the west terminal station. In other words, the traicsignals may be preceded by a monitoring signal having preferably apredetermined tone frequency modulation. This monitoring signal passesthrough the relay station the same as any traic signals and is revertedback after being keyed at the station of destination of the signals. Thereverted monitoring signal must, of course, be transmitted over channelshaving ydistinguishing carrier frequencies, as has been shown in thedescription of Fig. 5. The monitoring signals may be transmitted backthrough one or more relay stations tothe point of origin. Such a channelfor reverted signals may also be used, if desired, for continuousmonitoring of traffic signals but without the necessity for keying toidentify the station at destination.

Relay X also closes a circuit through its armature b for controlling aso-called transducer 22 by signals passed through the receiver R, sothat the incoming signals as demodulated may be applied as modulationsfor signals retransmitted by the transmitting unit T. Hence the outputside of the transducer 22 is connected to the input side of themodulating circuit of the transmitter T. An oscillator 23 delivers asuitable carrier frequency wave u to the transmitter and it is,therefore, seen that this wave may be suitably modulated by output fromthe transducer 22 and radiated from the antenna i6.

Details oi the transducers 22 and 25 are not herein given since they arewell known in the art. In some cases it may be desirable to employ apassive type of transducer 32 as shown in Fig. 5. This unit may consistof a reilector disposed so as to receive part of the energy radiatedfrom the antenna VI6 and to be reiiected toward the antenna l5. Testingof all the apparatus located at relay station A is then readilyaccomplished, even though it might be impossible to utilize the channelsbetween station A and station B.

It will be apparent that if the transducer 32 is to be used only fortest purposes, it should be rendered inactive during normal trafficconditions, especially when two-way communications are under way.Accordingly it will generally be arranged for such a reflector 32 to bemoved into and out of its functioning position in response to a remotecontrol signal of any suitable characteristic. Facilities foraccomplishing this result are well known in the art and need not befurther detailed herein.

Still other types of transducers and coupling circuits may be employedat each relay station, if desired. They will preferably includeamplifier systems where it is necessary to strengthen the receivedsignals before using the same to modulate an out-going wave.

The relay X also closes a circuit through its armature c for derivingreverted signals from the receiver R1, these signals being then passedthrough a back contact and armature g of relay L, to an inactive keyer2li, and thence to the input side of a transducer 25 connected totransmitter T1 whose antenna Il is aimed in a westerly direction. It maybe stated here that the keyer 2A plays no part in this circuit at thistime, it being normally positioned so as to provide a closed circuittherethrough.

When the transmission of a communication has been completed the relaystationapparatus may be brought to idle condition by the transmission ofa selector signal towhich the selector 1 will respond, this signal asshown being received on an ultra-high frequency wave collected by theantenna lli. The response to such signal is one which will restore tonormal either of the relays I8 and IQ, thus opening the operatingcircuits to the selector relays X or L.

When it is desired that the relay station shall operate for locallyrecording a communication or for utilizing trafiic signals in any otherdesired manner, a preliminary selector signal may be sent, to which theselector Z is responsive. This causes the relay I9 to operate forclosing a circuit from the battery 20 through the winding of relay L. Inthis case the following circuits are established ,for placing the relaystation in operative condition. Only the transmitter T1 is to beenergized in this case for reverting monitoring and other signals backto the west station. The power supply source 2l is, therefore, connectedthrough armature f of relay L and thence to the power supply terminal ofthe transmitter T1.

It is to be presumed that the signals to be sent to the relay stationwill serve either as monitoring signals for informing the operator atthe west station that the relay station is in operative condition, orelsefor recording at the relay station a given communication.Accordingly, I have shown auxiliary circuits to be also established, asY desired, bythe operation of the relay L. One of these circuits isclosed through armature d for causing an energy source 26 to drive amotor 21 whereby the keyer 24 is operated to superpose a signature codeupon the received monitoring signals.: The operation of the motor 2l maybe limited to a predetermined time by including in the motor circuit atime limit switch 23. Such switches are well known in the art and may beemployed in this connection for automatically breaking the motor circuitafter suiiicient time has been allowed for observing the monitoringsignals. The operation of the keyer 2Q is preferably one which willintroduce dots, dashes, or other code identification signals and applythe same to the incoming tone frequency signals as collected by theantenna lll. The path for such signals may now be traced througharmature g of relay L, thence through the keyer 2li and then to thetransducer 25 which causes the transmit- Y ter T1 to be modulated forreverting the monitoring signals from antenna lll to the west station.The incoming signals which are passed through the receiver R may also berecorded by passing the same'through the armature e and thence to arecorder 29.

Assuming that conditions have been found operative at the relay stationas noted by the reverted transmission of the keyed monitoring signals, amessage of any length may then be recorded at the unit 29 and thereafterthe relay station itself may be closed down by the reception of a stopsignal to which the selector r is responsive. This signal, as haspreviously been stated', operates to restore relay I9, thus releasingthe rel-ay L.

armature b of relay X to the transducer 22 which controls the modulationof transmitter T. Simultaneously sign-als originating at the eastterminal may be collected on antenna l5, received and detected byreceiver R1, passed through armature c of relay X, and thence throughthe back contact and armature g of relay L to the inactive keyer 24through which signals are passed to the transducer 25 for controllingthe modulation of transmitter T1 whereby the signals are sent out fromantenna I'I to the West terminal.

Various auxiliary selective apparatus and relays may also be used, ifdesired, for substituting, either automatically or upon reception of anactuating signal, certain stand-by equipment in a relay station forequipment which has failed to operate. The principles involved in theapplication of these selectors and circuit switching means aresubstantially illustrated by the selectors and relays shown in Fig. 9.For the sake of simplicity, therefore, they have not been added to thecircuit diagram.

As will be clearly understood by those skilled in the art, variousmodifications oi the invention itself are to be considered as fallingwithin the scope of the subject matter claimed. The invention is,therefore, limited only in accordance with the claims.

I claim:

1. In a radio relay system, a plurality of stations, radio links forestablishing communication from station to station, means including lowpower apparatus responsive to a start signal from a manned station forsetting up a predetermined operating condition at an un-manned station,selective means for causing signals received at said un-manned stationto be relayed forward to another station, means at the last mentionedstation for causing at least some of the signals received thereat to bereverted, and means operable in response to reverted signals received atsaid un-manned station from said other station for relaying saidreverted signals back to said manned station.

2. In a radio relay system, the combination according to claim 1, andmeans -for keying said reverted signals by a signature code whichidentifies the station where reversion of the signals takes place.

3. In a radio relay system, a. plurality of stations, radio links forestablishing communication from station to station, means including lowpower apparatus responsive to a start signal from a manned station forsetting up a predetermined operating condition at an un-manned station,selective means for causing signals received at said un-manned stationto be recorded, a transmitter and directive antenna operative topropagate a radiant energy beam in the direction of said manned stationand means controlled by signaling energy received at said un-mannedstation for modulating the output from said transmitter.

4. In a radio relay system having a plurality of stations andintercommunicating links therebetween, the method of testing eachintermediate station as to operativeness or failure which comprisestransmitting remote control signals, and monitoring signals from one endof the system to each succeeding station by relaying the same oversuccessive communication links, causing said monitoring signals to bereverted at the station beyond which a failure occurs, keying saidmonitoring signals by a signature code appropriate to the station wherereversion takes place, and transmitting the keyed signals back to thepoint from which the unkeyed signals originated.

5. In a radio relay system having a plurality of stations andintercommunicating links therebetween, the method of operating saidsystem as a two-way network which comprises transmitting remoteswitching control signals destined to be responded to at each successivestation, causing the response at each station to prepare two linkages,one ior retransmission of switching control signals, test signals andtraiiic signals through said station in one direction, the other forre.- transmission of test signals and traiiic signals through saidstation in another direction, drawing upon two carrier wave sources ateach intermediate station for desired retransmission of signals inappropriate directions, causing the signals received at eachintermediate station over one link to be retransmitted over another linkby modulating an appropriate wave from one of said carrier sources, andcausing said test signals to be reverted over any desired number oflinks to the point of origin.

6. In a radio relay system a plurality of stations, including terminal`stations and at least one relay station, each of said stations beingprovided with receiving and transmitting apparatus units and said relaystation being provided with remote control apparatus operable by signalsfrom a terminal station for starting and stopping various ones of saidunits, means at said relay station operable under control of testsignals sent out from the transmitting apparatus of a terminal stationfor modulating the output of a transmitting unit at said relay station,thereby to revert said test signals to the originating terminal station,means for so characterizing said modulated output as to indicate thethen existing condition of said apparatus units, and means includingsaid receiving apparatus at a terminal station for rendering themodulated test signals intelligible.

7. A system according to claim 6 and having means including directionalantennae connected with each apparatus unit at the several stations,whereby said signals are efficiently directed to their properdestination.

8. In a radio relay system, a plurality of stations each havingreceiving and transmitting apparatus units, a directive antennaconnected to each unit and suitably aimed toward an antenna appropriateto a different station, remote control apparatus at a given one of saidstations comprising aradiant-energy-responsive-cold-cathode-discharge-tube-relay forrendering at least one of said apparatus units operative, other remotecontrol apparatus at said given station responsive to appropriatesignals from a remote station for effecting a desired set of circuitconnections between different receiving and transmitting apparatusunits, means including a suitably disposed radiant energy reector forreceiving from one said antenna and re-radiating toward another saidantenna at said given station signals originating at a remote station,means for reverting said signals by transmission thereof in thedirection of said remote station, and means at said remote stationresponsive to said reverted signals for giving an indication as to thecharacter of the operating conditions established at said given station.

ALFRED N. GOLDSMITH.

